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Any one knowing why type of aircraft or its basic used, please email me. I'm curious about the bay window on the first officers side at the rear.

What you've taken a photo of is the Air Force's C-145A, also known as the PZL M28 Skytruck. This aircraft is manufactured in Poland by PZL Mielec and powered by Pratt & Whitney PT6A-65B turboprops.

This excerpt from the U.S. Air Force's page regarding their C-145A should give you direct insight into its use and that "bay" window -

"The C-145A’s primary role is to support U.S. Special Operations Command’s Aviation Foreign Internal Defense mission to assess, train, advise and assist foreign aviation forces in airpower employment, sustainment and force integration. Secondly, the C-145As provide the theater Special Operations Commands a light mobility capability."

http://www.af.mil/AboutUs/FactSheets/Display/tabid/224/Article/467765/c-145a.aspx